This invention relates to a method for producing galvanized metal sheet or strip material having a zinc coating on one side only. More particularly, this invention relates to a method for treating zinc-coated metal strip or sheet material so as to remove the zinc coating from one side thereof while simultaneously depositing a substantially equivalent amount of zinc on the opposite side.
The use of galvanized metal sheet or strip material is conventional in many applications where corrosion resistance is important. However, in some cases, particularly when used in automobile body construction and the like, it is undesirable to have a zinc coating on both sides of the metal sheet or strip since such a coating has an undesirable effect on the weldability and surface finishing of the metal. In such instances it is important to provide a material having a galvanized surface on one side of the metal sheet, which side is generally unprotected otherwise, and a clean surface on the opposite side for efficient weldability and cosmetically acceptable surface finishing, such as painting.
Efforts to provide such galvanized sheet metal in the past have taken many forms including, for example, that of U.S. Pat. No. 2,894,850 to Green. Green describes a process which, in effect, includes masking one side of sheet metal with an aluminate coating to prevent the adherence of zinc thereto. U.S. Pat. No. 3,178,305 to Ward in part describes a process for electrolytically stripping one side of a zinc coated steel strip to provide a galvanized product having a zinc coating on one side only, but the strip itself is made anodic and the stripped zinc becomes deposited on the cathode. No provision is made for simultaneously depositing an equal amount of zinc onto the opposite side of the treated strip.